FINAL DIAGNOSIS: INFECTION OF LYMPH NODES AND MEDIASTINAL SOFT TISSUE WITH Mycobacterium szulgai
Mycobacterium szulgai was first reported as a species in 1972 and is named for the Polish microbiologist T. Szulga.(1) Infections with Mycobacterium szulgai are extremely rare, but cases are increasingly being noted primarily in patients with impaired cellular immunity (i.e., transplant recipients, HIV+ individuals) and in middle-aged to elderly patients with pre-existing lung disease. Although M. szulgai has been implicated in infections of many different bodily sites, ranging from a granulomatous olecranon bursitis to cutaneous infection, a case of M. szulgai osteomyelitis in an AIDS patient was recently reported.(2) Pulmonary infection clinically indistinguishable from M. tuberculosis infection is the most common manifestation.(3) Clinically, Mycobacterium szulgai infection is indistinguishable from classic infection with M. tuberculosis. Common presentations include fever, night sweats, weight loss, and a cough with or without hemoptysis.. A retrospective study of the period 1981-83 reviewing reported cases of nontuberculous mycobacterial infections in the United States included 24 (0.57% ) cases of M. szulgai infection (all sites) out of a total of 4201, corresponding to approximately 0.01 cases/100,000 population for that time period.(4)
Clinical distinction between infection with M. szulgai and tuberculosis and other nontuber-culous mycobacterial infections is not possible. Definitive diagnosis requires isolation and identification of the causative agent. On acid-fast stain of the organism, M. szulgai may exhibit some banding, such as that seen with M. kansasii. M. szulgai is a scotochromogen, producing an orange pigment both in the dark and in light.(5) A unique feature of pigment production in M. szulgai is the temperature-dependent nature of this phenomenon. When grown at body temperature (37oC), the organism is scotochromogenic, but at 25oC, the pigment is only produced in a lighted environment (e.g., the organism is photochromogenic). This places the organism in the Runyon group II classification of mycobacteria. Another characteristic of M. szulgai is relatively rapid growth in culture, with production of smooth or rough colonies on solid media within 2 weeks. Biochemical tests will help further differentiate the organism. M. szulgai will display the following reactions (5), in contrast to other scotochromogens (M. scrofulaceum, xenopi, and gordonae):
M. szulgai is commonly susceptible to standard antituberculous agents, but treatment in each case should depend upon evaluation of susceptibility for the organism. In this case, the organism was susceptible to many agents commonly used for the therapy for Mycobacterium tuberculosis infection.
Contributed by Kevin D. Horn, MD and William A. Pasculle, ScD